I would also advise that you read more. Pick up a novel that you find interesting. The more you expose yourself to well written English, the better your English will become.
Just out of curiosity, can you point out these errors?
HTH :)
And if anyone wishes to see the changes: paste both texts into http://www.quickdiff.com/index.php and hit 'Compare'
Okay, if any of you actually went through the exercise of pasting it onto quickdiff.com, you probably noticed how aggravating it was to copy & paste from that container. Really a bigger turn-off in terms of UI than his English skills, in my opinion.
http://www.solipsys.co.uk/new/LearningLanguages.html?HN
I went to the local shops and bought a copy in Bulgarian of "Men At Arms" by Terry Pratchett, and I set about decrypting it.
As you might expect, I didn't really get all that far in four days, but I was able to go to the local shops and order coffee, comment on the weather, reply to questions about my work, and read the menu. I could also do some actual shopping, with considerable tolerance from the vendors, no doubt, but without anything other than Bulgarian and good will.
We had a formal dinner at the end, and as the Rear Admiral came down the line shaking hands I said "Blagodarya" (can't write Cyrillic) and he stopped dead in his tracks. "You speak Bulgarian?" he asked, in tones of great surprise. "Only a few hundred words - I've only been here 3 days" was my reply. He proceeded to quiz me on common phrases, and seemed surprised and impressed.
Later, when we all got a "Thank You" email, I was the only one whose email was personalised. More, even though that contract was never awarded, we have since been contacted to start negotiations for other work. Clearly the episode made an impression.
Sadly, after leaving I didn't have the chance to continue practising and I lost it all quite quickly, but there was a magic period of a few hours where I was really getting the hang of communicating (comprehension was significantly better than synthesis), and it has made me regret again my mono-lingual background.
For many people it won't matter much, but for a few it definitely will. You need to decide how much it matters to you, and if you decide it matters, you need a copy-editor. You don't want someone to write the copy, you just want someone to tidy it up and remove the worst of the errors without changing the content much.
What contacts do you have? My circle of contacts would, for me, each copy-edit a few hundred words a fortnight. Depending how much I wrote, that would probably be enough without imposing on them too much. I'd also then buy them a beer, or cook them a meal every couple of weeks to say thank you.
There are also tools such as the Link Grammar. After spell checking, type what you want into that and see if you get one parse. If so, you're done. It's easy to download and install, and not so hard to automate.
That would be my recommendation.
PS: I'm a complete grammar-nazi and am probably much more severe than most people. Trust me - it was pretty good.